Godot-ci update script

[abarichello]

Since Docker Hub's automated builds are now locked behind a $60/year plan creating a script to check for new godot releases everyday would help keep this project up to date with minimal manual intervention.

Workflow:

1. Check for a new godot release everyday.
2. If a new release is available build the docker image with the GODOT_ENV variable updated.
3. Commit a new tag and create a new GitHub release in this repository.

[Razzlegames]

I was thinking... You could run a Github action on a schedule to accomplish this.

https://jasonet.co/posts/scheduled-actions/

The action workflow can publish the latest Docker image to DockerHub, using an access token you create through your DockerHub account.

I think it shouldn't cost anything (other than time), but I imagine there are limits. I did this with wercker pipelines, fairly recently (not a fan of their config setup, as it's not all in code).